Plasminogen activators convert plasminogen to the active form of the enzyme, plasmin, which catalyzes the digestion of fibrin clots. Plasminogen activators such as streptokinase and tissue plasminogen activator (TPA) have been approved by the Food and Drug Administration for thrombolytic therapy in the treatment of coronary and pulmonary thrombosis. These proteases may also be used in the solubilization of fibrin clots formed when catheters or shunts are in place for long periods of time. The use of plasminogen activators has saved countless lives through activating plasmin, which in turn, dissolves artery-clogging blood clots.
On the other hand, the presence of active plasmin in the serum for long periods of time or the accumulation of active plasmin can lead to serious consequences, such as uncontrolled bleeding. Thus, the use of plasminogen activators are not without side effects. Due to the requirement of the relatively large quantities of plasminogen activator for effective therapy and the resulting generalized lytic state of the serum, the patient is always at risk of bleeding. This risk is lower with TPA, because of the specific fibrin binding activity of this enzyme. However, because of the relatively high doses required to treat coronary artery thrombosis, bleeding still occurs in a number of patients. In addition, in the case of coronary artery thrombosis, re-occlusion of the blood vessel following successful clot lysis occurs in a number of patients. Furthermore, TPA has been shown to have a relatively short half life in vivo. This is a particular problem since blood plasma naturally contains a potent inhibitor of plasmin, .alpha..sub.2 -antiplasmin, which can counteract the life-saving ability of TPA, if TPA is administered at lower doses. Finally, TPA is very expensive and some Healthcare providers will not authorize the use of the TPA in lieu of its less-specific analogs because of financial concerns.
Recently, a plasmin binding molecule from the surface of an untypable clinical strain of group A streptococci has been reported [Lottenberg et al (1992) J. Bacteriol. 174: 5204-5210, See also U.S. Pat. No.5,237,050 dated Aug. 17, 1993 and its continuation U.S. Pat. No. 5,328,996, dated Jul. 12, 1994]. This protein is structurally similar to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). This protein has been described as having plasmin-binding activity and could possibly be administered to increase fibrolytic activity. A novel 35.8 kDa multifunctional protein on the surface of group A streptococci has also been reported. This protein (streptococcal surface dehydrogenase, SDH) was also found to be structurally and functionally related to GAPDH [Pancholi, V. and Fischetti, V. A. (1992), J.Exp.Med. 176: 415-426]. In contrast to the finding of Lottenberg et al (see supra), however, SDH was found to bind very weakly to plasmin and plasminogen.
On the other hand, a molecule having homology with .alpha.-enolase recently has been described to be a plasmin receptor on human carcinoma cells [Lopez-Alemany, R. et al (1994), Thrombosis Research 75:371-381]. Enolase is a 2-phospho-D-glycerate hydrolase (hydrolyase) (E.C. 4.2.1.11), that catalyzes the dehydration of D-glycerate-2-phosphate to yield enolpyruvate phosphate (phosphoenolpyruvate). Three classes of isoenzymes have been identified in mammalian tissues. Each enzyme is a homodimeric protein composed of two .alpha., .beta., or .gamma. subunits [Zommzely-Neurath, C. E., 1983 in Hand book of Neurochemistry, ed Lajtha, A. (Plenum Press New York), 2nd ed, vol 4, pp. 403-433]. Isoenzyme .alpha. is present in most tissue, .beta. is localized in muscle tissue and .gamma. is found only in nervous tissue. Although, enolase has been generally found in the cytosol, Miles and his group recently reported that the .alpha.-isoform of enolase is a candidate for being a plasminogen receptor on U937 monocytoid cells [Miles, L. A. (1991) Biochemistry 30,1682-1691], and also for being on the surfaces of peripheral blood monocytes and neutrophils [Redlitz et al, (1995) Eur. J. Biochem. 227:407-415]. However, enolase has never been identified on the surface of bacteria.
Group A streptococci (Streptococcus pyogenes) are the causative agent for many suppurative infections in humans, most notably pharyngitis, impetigo, scarlet fever and more recently, invasive disease such as necrotizing fascitis. The Centers for Disease Control estimate that &gt;35 million cases of pharyngitis occur in the U.S. each year. The incidence of group A streptococcal respiratory infection rises sharply at age four, peaks at age six, and declines above age ten, reaching adult levels by 18 years [Fischetti et al., J.Exp.Med, 133:1105-1117(1971)]. At its peak incidence, as many as 50% of children between the age of five and seven suffer from streptococcal infection each year. Approximately 3-5% of individuals with untreated or inadequately treated streptococcal pharyngitis may develop acute rheumatic fever (Fischetti, 1971, supra). Although antibiotic treatment (primarily penicillin) has reduced the overall frequency of rheumatic fever in the U.S., several outbreaks have been reported in Utah [Veasey et al.,N.Engl J Med, 316:421-7 (1987)],[Veasey L G et al., J.Pediatr,Jan. 9-16 , 1994] Pennsylvania [Wald E R et al.,Pediatrics, 80:371-4(1987)], and Ohio [Congeni, B. et al.,J. Pediatr,111:176-99 (1987)]. The recent appearance of streptococcal-associated toxic shock syndrome, and severe tissue necrosis may be indicative of increased or altered virulence of certain strains [Stevens D L et al., N. Engl.J.Med., 321:1-7 (1989)]. No effective vaccine for group A streptococci is available despite more than 50 years of continuous effort. This may in part be due the finding that only type-specific antibodies to the surface M protein are opsonic, and &gt;80 different serotypes of M protein have been identified. Early attempts at vaccine development have resulted in only type-specific protection [Fox En et al., J. Clin Invest, 52:1885-92, (1973)] [Beachey E H et al., J. Exp. Med, 150:862-77 (1979).
Thus, agents that can be used in combination with plasminogen activators to improve their specific therapeutic action while diminishing their side effects are needed. Similarly, agents that can lower the cost of thrombolytic therapy by lowering the amount of TPA required are also needed.
In addition, methods for immunizing people against pathogenic group A streptococci are needed.
The citation of any reference herein should not be construed as an admission that such reference is available as "Prior Art" to the instant application.